Can't get remote Wake On Lan working on ReadyNAS Ultra2Plus with OS6

I don't see how this can be the NAS, since it has no idea if the WoL packet is coming from the internet or coming from the local LAN.

But it's also clear that the packet is arriving at the router.  It's possible that the router has lost track of which ethernet port the NAS is connected to, so it doesn't know how to deliver the packet.  Is the router on a power schedule?

You could try reserving the IP address in the router, instead of configuring a static address in the NAS.  Not sure if that will help or not, but it does no harm (and in my opinion address reservation is a better way to manage IP addresses).

But you might need to go with a power schedule on the NAS (either instead of or in addition to the WoL).  If the router turns on for an hour perhaps 2x a day, then the router might not lose track of it.